Add compile-time format string checks to format_to (#783)

Author: vitaut

include/fmt/format.h

@@ -3524,19 +3524,16 @@ inline wformat_context::iterator vformat_to(
   return vformat_to<arg_formatter<range>>(buf, format_str, args);
 }
 
-template <typename... Args, std::size_t SIZE = inline_buffer_size>
+template <typename String, typename... Args,
+          std::size_t SIZE = inline_buffer_size>
 inline format_context::iterator format_to(
-    basic_memory_buffer<char, SIZE> &buf, string_view format_str,
+    basic_memory_buffer<char, SIZE> &buf, const String &format_str,
     const Args & ... args) {
-  return vformat_to(buf, format_str, make_format_args(args...));
-}
-
-template <typename... Args, std::size_t SIZE = inline_buffer_size>
-inline wformat_context::iterator format_to(
-    basic_memory_buffer<wchar_t, SIZE> &buf, wstring_view format_str,
-    const Args & ... args) {
-  return vformat_to(buf, format_str,
-                    make_format_args<wformat_context>(args...));
+  internal::check_format_string<Args...>(format_str);
+  typedef typename internal::format_string_traits<String>::char_type char_t;
+  return vformat_to(
+        buf, basic_string_view<char_t>(format_str),
+        make_format_args<typename buffer_context<char_t>::type>(args...));
 }
 
 template <typename OutputIt, typename Char = char>